Polyolefins generally have advantages such as excellent moldability, heat resistance, mechanical properties, hygienic qualities, water vapor permeation resistance and appearance of molded articles thereof, and hence they are broadly used for extrusion molded articles, blow molded articles and injection molded articles.
The polyolefins, however, contain no polar group in the molecule, so that they have low compatibility with polar resins such as nylon and EVOH and low adhesion properties to polar resins and metals. Therefore, it is difficult to use the polyolefins by blending or laminating them with these materials. In addition, molded products of the polyolefins have problems of poor surface hydrophilic properties and poor antistatic properties.
To solve such problems, there has been heretofore widely used a method of grafting polar group-containing monomers on the polyolefins through radical polymerization to enhance affinity for the polar materials.
Engineering plastics such as nylon have excellent heat resistance and strength, and hence they are used for electronic/electric parts. The engineering plastics such as nylon generally have low impact resistance, so that they are sometimes blended with olefin copolymers to improve the impact resistance.
The polyolefins, however, contain no polar group in the molecule and show low compatibility with polar resins, and therefore a method of grafting polar monomers on the polyolefins to improve compatibility with the polar resins has been heretofore widely used.
In this method, however, intermolecular crosslinking of polyolefins and breaking of molecular chains take place with the graft reaction, and hence viscosity matching of the graft polymer and the polar resin is difficult, and satisfactory compatibility is not obtained in some cases. Further, a gel component produced by intermolecular crosslinking or a foreign matter (foreign matter attached to a lip of a die) produced by breaking of molecular chains may cause bad appearance of the molded products.
In Japanese Patent Laid-Open Publications No. 259012/1989, No. 259012/1989, No. 51510/1990, No. 51511/1990 and No. 177403/1991, a process comprising copolymerizing an α-olefin and a polar group-containing monomer using a Ti catalyst or a V catalyst is described. According to this process, intermolecular crosslinking and breaking of molecular chains hardly take place, but in the use of these polymerization catalysts, the resulting copolymer has an ununiform molecular structure such as wide molecular weight distribution or high inversion content. On this account, orientation of the polar groups toward the interface between the copolymer and the polar material may be unsatisfactory, and adhesion properties to the polar materials and compatibility therewith may be insufficient. In the use as a composition, effects in adhesion properties and compatibility are not exhibited unless a graft copolymer is added in a large amount.
In order to enhance surface hydrophilic properties and antistatic properties, a method of adding a small amount of a low-molecular weight surface active agent to the polyolefin and molding the mixture has been used. In this method, however, the added surface active agent bleeds out on the surface, and after molding, the film surface sometimes has a problem of whitening. The surface active agent having bled out on the surface runs off together with water droplets sticking thereto, so that a problem that effects by the surface active agent do not last long may take place.
The present inventors have studied in the light of the above problems. As a result, they have found that a copolymer having a specific molecular structure and a composition containing the copolymer are excellent in compatibility with polar resins and adhesion properties to polar resins and metals, and they have also found that the copolymer and the composition have excellent surface hydrophilic properties and antistatic properties. Moreover, the present inventors have found the copolymer and the composition can be favorably applied to various uses.
As a process for preparing an olefin polymer such as an ethylene homopolymer, an ethylene/α-olefin copolymer, a propylene homopolymer or a propylene/α-olefin copolymer, a process comprising polymerizing an olefin in the presence of a titanium catalyst comprising a solid titanium catalyst component containing magnesium, halogen and an electron donor, and an organoaluminum compound, or a vanadium catalyst comprising a vanadium compound and an organoaluminum compound has been heretofore known. In the copolymerization of a polar monomer using such catalyst, there reside problems that the molecular weight distribution or the composition distribution is wide and the polymerization activity is low. As disclosed in Japanese Patent Laid-Open Publications No. 259012/1989, No. 51510/1990, No. 51511/1990 and No. 177403/1991, when an olefin and a polar group-containing monomer are copolymerized using a Ziegler catalyst to prepare, for example, a polyolefin containing a polar group, polymerization at low temperatures is only carried out, so that this process is known to have a problem of low activity. It is generally known that an olefin is polymerized in the presence of a metallocene catalyst comprising a transition metal compound such as zirconocene and an organoaluminum oxy-compound (aluminoxane). It is also known that if the metallocene catalyst is used, an olefin polymer having a high molecular weight is obtained with high activity and the resulting olefin polymer has narrow molecular weight distribution and narrow composition distribution.
As a process for preparing a polyolefin containing a polar group, a process using a metallocene catalyst is also known. For example, it is publicly known that polymerization of an OH group-containing olefin is conducted using a metallocene compound having a ligand of non-crosslinked cyclopentadienyl group, crosslinked or non-crosslinked bisindenyl group, or ethylene crosslinked unsubstituted indenyl group/fluorenyl group, as described in Macromolecules, 28, 5351 (1995), Macromolecules, 29, 5255 (1966), and Polymer Preprints, Japan, 49(2), 215 (2000).
If is publicly known that polymerization of an olefin having NR2 (R: alkyl group) as a polar group is conducted using a metallocene compound having a ligand of non-crosslinked cyclopentadienyl group, crosslinked or non-crosslinked bisindenyl group, or crosslinked unsubstituted indenyl group/cyclopentadienyl group, as described in Macromolecules, 31, 2019 (1998) and Macromolecules, 32, 14 (1999).
A process using an organometallic compound other than the metallocene compound is publicly known, as described in Science, 287, 460 (2000), OCOP2000 at Oslo, and Books of Abstracts (C. W. Chien). These processes, however, have a disadvantage of extremely low polymerization activity.
On this account, protection of the polar group by a protective group is carried out. A method of protection is described in, for example, Macromolecules, 31, 2019 (1998), J. Am. Chem. Soc., 114, 9679 (1992), Polymer Preprints, Japan, 49(2), 209 (2000).
In the above processes, however, the protective group is introduced, and after the reaction, the protective group must be removed, so that the operations are complicated.
Under such circumstances, the present inventors have studied and found that an olefin polymer containing a polar group can be prepared with high polymerization activity by copolymerizing an olefin and a polar group-containing monomer in the presence of a transition metal catalyst into which a cyclopentadienyl group or other special ligands have been introduced, without using radical polymerization or a Ziegler polymerization catalyst. Based on the finding, the present invention has been accomplished.
A method of selectively introducing the polar group at only one end of the polymer chain or inside of the main chain and at one end of the main chain has been heretofore unknown. Then, the present inventors have found a method of selectively introducing the polar group at only one end of the polymer chain or inside of the main chain and at one end of the main chain, and accomplished the present invention.